1. Field of the Invention
The subject invention relates to methods and apparatus for precision guiding a web and, for instance, has utility in magnetic tape transports, photographic film handling apparatus and other web transporting or handling equipment wherein a precision guiding of a tape, film or other web is required or desired.
2. Description of the Prior Art
Throughout the years, many precision guiding techniques and apparatus have been proposed. By way of example, and not by way of limitation, precision of a web is important in information processing or handling equipment wherein a web-shaped information carrier is to be accurately positioned relative to information recording and playback devices.
One type of prior-art web guiding system may be seen from U.S. Pat. No. 2,989,265, by W. T. Selsted, issued June 20, 1961, U.S. Pat. No. 3,434,639, by C. D. Cowles, issued Mar. 25, 1969, and from an article by Stephen E. Amos, entitled Self-Adjusting Belt Guider, Magazine of Machine Design, November 1953. This type of web guiding system is unsuitable for present purposes because of its inherent facility of adjusting the moving web in either lateral direction.
Another type of web guiding system, exemplified by by U.S. Pat. No. 3,143,270, by N. B. Cohen, issued Aug. 4, 1964, provides a single-edge guide for the moving web, but employs specially shaped guides which impose considerable wear on the tape.
A further type of web guide is apparent from U.S. Pat. No. 3,281,040, by F. F. Grant, issued Oct. 25, 1966. According to that proposal, a positive pressure gradient is established at the guiding element so that the moving web tends to slide "downhill" of the gradient and the edge of the web adjacent a guiding shoulder is brought into contact with that shoulder. Web guides of this type are useful in some applications but tend to be relatively long, bulky and air consumptive.